Dune slacks are seasonal wetlands, high in biodiversity, which experience considerable within -year and between-year variations in water table. They are subject to many pressures including climate change, land use change and eutrophication. Despite their biological importance and the threats facing them, the hydrological and nutrient parameters that influence their soil properties and biodiversity are poorly understood and there have been no empirical studies to date testing for biological effects in dune systems resulting from groundwater nutrients at low concentrations, along with the interaction of lowered water tables. In this study we examined the impact of groundwater nutrients on water chemistry, soil chemistry, soil enzyme activity, greenhouse gas fluxes, vegetation composition and plant tissue chemistry. Experimental work was either; 1) undertaken at a designated sand dune site prote cted for its nature conservation interests (Aberffraw, North Wales, Anglesey, UK) or 2) a mesocosm experiment and laboratory assays using material collected from this site. Our findings identified that dune slack habitats are vulnerable to nitrogen groundwater contamination from concentrations as low as 0.2 mg l-1, a concentration described as 'no cause for concern' on dune slack habitats by the E cohydrological guidelines for wet dune habitats. These concentrations were seen to increase soil nitrate concent rations and increase nitrophilous species whilst decreasing basipholous species. Our study also suggests that these impacts are likely to be intensified by climate change or water abstraction, as lowered water tables decreased denitrification rates which subsequently increased soil nitrogen concentrations. The uptake, processing and accumulation of nitrogen within sand dune systems increased from groundwater nitrogen contamination, where soil nitrogen concentrations, plant tissue nitrogen content and denitrification rates increased We also demonstrate a combination of chemical, microbial and fluorescent techniques to help identify potential nutrient contamination sources and pathways, which in turn, can inform appropriate management plans. These findings highlight the necessity toconsider groundwater nutrient inputs in addition to atmospheric nitrogen inputs in wetland systems when considering nutrient impacts.